Many thermoplastic products, including closures for bottles and jars, are produced from a thermoplastic material at a moldable temperature by injection molding, a process that is generally described in commonly-assigned U.S. Pat. No. 6,402,503 B1 (Hickman), the disclosure of which is incorporated by reference herein. A problem exists in manufacturing annular thermoplastic products by injection molding, however, in that known types of injection molding apparatus for annular products, for example, apparatus of the type described in U.S. Pat. No. 6,179,604 B1 (Takeda), tend to introduce moldable thermoplastic material under pressure into a flow path that leads to the injection mold in multiple streams around the circumference of the flow path. This leads to a characteristic known as weld lines where thermoplastic material from separate streams tends to weld or fuse together, and such weld lines tend to be locations of weakness in the molded products as a result of stress concentrations at the weld lines; they also tend to lead to dimensional distortion of the molded product as a result of uneven stress and shrinkage within the thermoplastic material from different streams in the molded product. Certain disadvantages of weld lines in a molded tubular product are described in U.S. Pat. No. 4,942,010 (Baker), and these disadvantages also apply to injection molded annular thermoplastic closure elements, such as the closure element 12 of the dispensing closure of my co-pending U.S. patent application Ser. No. 10/058,445, and probably also to injection molded annular gears, such as the gear 1 of the aforesaid U.S. Pat. No. 6,179,604 B1.